Vision correction is on the verge of a revolution. New technologies to measure the aberrations or distortions in the optics of the eye will soon be available to the public. These new wavefront measurement techniques such as Shack-Hartmann wavefront sensing and Talbot Interferometry can precisely measure the eye's aberrations so that vision may be corrected up to 20/10. Wavefront sensing is the method for rapidly and accurately assessing aberrations in a patient's eye to create a customized prescription for correction.
Once the aberrations have been measured, using conventional methods or by wavefront sensing, the measurements must then be transferred into a vision correction system, such as, spectacles, contact lenses or the patient's eyes. Recent advances in spectacle manufacturing and laser refractive surgery techniques such as LASIK now enable the creation of highly accurate corrective prescriptions for individuals. However, this is not the case with respect to contact lenses. Popular soft contact lenses cannot achieve the same result as spectacles or laser refractive surgery because of dimensional variations in fabrication. Hard contact lenses, which may provide the platform to achieve the results of spectacles, are not as comfortable as soft contact lenses and lack the necessary positional stability on the eye. Hybrid hard-soft contact lenses comprising a hard center portion and a relatively soft outer skirt have been developed to provide a platform for a corrective prescription and also provide the comfort of soft contact lenses. Contact lenses that exhibit high oxygen permeability are generally preferred for the health and comfort of the eye.
Myopia, or nearsightedness, is a condition wherein the axial length of the eye is too long, or the crystalline lens is too strong. As a result, the image of distant objects is brought to a focus in front of the retina such that the image is out of focus before the light strikes the retina. The prevalence of myopia is reaching epidemic proportion globally with an incidence of approximately 25% in the United States and Western Europe to as high as 90% in urban Chinese. The incidence of myopia has been shown to be greater in those persons having a college education. In addition, there is a high correlation between the age of commencing concentrated detailed tasks within arms length and the prevalence and degree of myopia.
Many causative factors for myopia have been suggested, including sustained close work, poor nutrition, the limitation of aerobic exercise, and stress resulting in increased tone in the sympathetic nervous system. Animal studies have established the ability to induce myopia in vertebrates and primates by causing the eye to sustain focusing. This suggests that it may be possible to decrease the progression of myopia through limitation of the focal demand using long term cycloplegia. Additional studies have indicated that the major anatomic factor tied to myopia is axial length, rather than the refractive power of the cornea or the crystalline lens of the eye. There is evidence that the rays of light falling on the far periphery make no contribution to the stimulus for axial length growth. Rather, the nature of the focus of the light on or near the macula is a probable contributor.
The application of adaptive optics has resulted in the development and commercialization of wavefront sensors or aberrometers that measure higher-order aberrations of the human eye. These instruments allow for the quantification of third order aberrations including coma and trefoil, fourth order aberrations including spherical aberration and quadrafoil and higher-order aberrations. A study of pilots with visual acuity better than 20/20 along with excellent visual performance demonstrated the presence of 0.2 micron over 6 mm of vertical coma and 0.1 micron over 6 mm of positive spherical aberration. Further, a study of a population of Asians having myopia demonstrated a lesser amount of each of these aberrations. People having myopia typically are treated with spectacles and/or contact lenses. However, conventional spectacles and contact lenses are designed to correct only low order aberrations.
Hysteresis of the cornea involves the modulus of the cornea, or the ability of the cornea to flex and alter its geometry. Studies have indicated a correlation between myopic eyes and greater hysteresis. When an eye focuses on a close image, greater hysteresis allows the ciliary muscle to exert a force on the sclera and cornea, thereby producing an increase in corneal eccentricity. This increase in corneal eccentricity decreases spherical aberration, which produces a signal that stimulates axial length growth.
Studies of myopic eyes indicate higher eccentricity in the anterior corneal surface with a resultant decrease in spherical aberration. Hyperopic eyes tend to be more spherical with higher spherical aberration, and may remain hyperopic (i.e., too short for their optical system) because axial length growth is impeded when the signal from the paracentral wavefront is too far in front of the plane of focus.
U.S. Pat. No. 6,086,204 to Magnante teaches a method of fabricating contact lens surfaces or corneal surfaces to correct optical aberrations in a patient's eye. The method involves measuring the eye's optical aberrations, performing a mathematical analysis on the eye's optical aberrations and fabricating an aberration-correcting surface on the contact lens or corneal surface. However, Magnante does not disclose the intentional creation of higher-order aberrations to provide a preventive measure to reduce or eliminate the progression of myopia.
U.S. patent application Ser. No. 2004/0237971 to Radhakrishnan et al. discloses a method for controlling optical aberrations to alter modulation transfer functions. An ocular system is provided comprising a predetermined aberration-controlled design for producing corrective stimuli to alter accommodative lag and abate the progression of myopia. However, Radhakrishnan does not disclose the intentional creation of a predetermined aberration pattern comprising a positive spherical aberration that produces a wavefront error in which the paracentral wavefront is disposed in front of the retina.
Therefore, there exists a need for methods and apparatus for reducing or eliminating the progression of myopia.
There also exists a need for methods and apparatus for creating higher-order aberrations in a lens-eye system to provide a preventive measure to reduce or eliminate the progression of myopia.
There further exists a need for methods and apparatus for determining children that are most at risk for developing myopia.
There further exists a need for methods and apparatus for the intentional creation of a predetermined aberration pattern in a lens-eye system, wherein the predetermined aberration pattern comprises a positive spherical aberration that produces a wavefront error in which the paracentral wavefront is disposed in front of the retina.